The present invention relates to solventless platinum catalyzed silicone compositions convertible to pressure sensitive adhesives (PSAs) and method for making. More particularly, the present invention relates to the use of a spray dried silicone resin powder having triorganosiloxy units (M) and tetrasiloxy units (Q) and a PSA network mixture of a substantially linear alkenyl siloxane, a substantially linear silicon hydride siloxane and a hydrosilylation catalyst.
As shown by Hahn et al, U S. Pat. No. 3,983,398, platinum catalyzed organopolysiloxane compositions convertible to PSAs comprising a benzene soluble resinous copolymer of triorganosiloxy units and tetrasiloxy units have been used in the form of an organic solvent solution in combination with a network mixture. The network mixture consists of a substantially linear alkenyl siloxane or vinyl siloxane, a substantially linear silicon hydride siloxane and a hydrosilylation catalyst, such as a platinum catalyst.
Although PSAs can be made utilizing a combination of the above-described benzene soluble ingredients, prior to the present invention such PSAs required the stripping of organic solvent from the resinous copolymer while it was in the presence of a silicone fluid, such as a vinyl siloxane fluid. In most instances, the platinum catalyst also was present with the vinyl siloxane fluid during the stripping procedure. Stripping of an organic solvent by a heat curable silicone fabricator who did not have adequate solvent trapping equipment, generated volatiles which often resulted in excessive air pollution. The benzene soluble resinous copolymer was normally available to the fabricator as an organic solvent dispersion, because it could not be readily blended in bulk form into the network mixture. The term "network mixture" hereinafter means one or more of the silicone components comprising the mixture of alkenyl siloxane, a silicon hydride siloxane and a platinum catalyst.
Prior to the present invention, a convenient technique was to blend one or more of the network ingredients, such as the alkenyl siloxane, along with the platinum catalyst into an organic solvent dispersion of the benzene soluble copolymer. When the organic solvent was stripped, a workable silicone blend could be formed which could be formulated with additional heat curable silicone mixture ingredients. The stripping of organic solvent by a fabricator however, is environmentally unattractive particularly if inadequate solvent trapping equipment is used.
In addition to being environmentally hazardous, the use of an organic solvent dispersion of the benzene soluble copolymer with other network ingredients can often interfere with the ability of PSA fabricators to tailor make the PSA to the needs of the customer. It would be desirable therefore to provide readily blendable ingredients for making platinum catalyzed PSAs, potting compositions, vibration damping compositions and flexible casting resins comprising benzene soluble copolymers and network ingredients while at the same time, reduce environmental risks.
As taught in copending application, RD-22,105, organosiloxane hydrolyzate comprising chemically combined triorganosiloxy units and tetrasiloxy units can be spray dried to form a free-flowing silicone resin powder which is dispersible in silicone fluids.